The invention is of an improved kind of pressure valve meant for oil wells producing by gas lift.
At wells equipped to produce by means of gas lift, valves known as "pressure valves", also "calibrated valves" or also, "charged bellows valves" are usually employed. In wells where continous gas lift is employed such valves are generally used to start up a well, that is, to start up production again after it has been stopped for some reason. Where gas lift is intermittent this kind of valve is also used for regular working of a well.
Lately, however, these valves have been used for satellite wells producing by continuous gas lift. At such wells any break in operation is extremely expensive and therefore avoided to the utmost. Therefore the production string lowered with the valves is meant to operate for a relatively long time, which means that the point at which gas has to be injected will be a different one as time goes by. Hence, neither a pressure valve can be used just for start-up nor an "aperture valve" for regular operation, as usually happens where the wells are of the continuous gas lift sort. Pressure valves have to be used.
Pressure valves were suitable for the first two major applications therewith (start-up for continuous gas lift well and start-up as well as regular operations for intermittent gas lift wells). However they are not suitable for satellite wells.
Much study has been undertaken concerning the behaviour in action of these valves for this became important to know in the designing of continous gas lift wells, where such valves are used for regular operation. However such study is complicated and so far full mastery over behaviour has not yet been achieved, in spite of exhaustive experimental surveys undertaken throughout the world.
It seems pretty obvious to us that it is unlikely that such knowledge will be forthcoming in the near future at the rate such usual kind of approaches are taking place. Thus since we have not been able to well determine the behaviour of this kind of valve in operation it seems reasonable that the best approach is to develop a valve with the desired behaviour.